1. Field of Invention
The present invention relates to equipment that transmits and receives data and a data compression method. Particularly, it relates to an improved data transmitter/receiver apparatus that is best applied when remotely operating a remote host computer over a LAN (local area network).
2. Background Technology
Conventionally, when remotely operating a remote host computer over a LAN, it is necessary to transfer the screens of the remote host computer to the terminal performing the remote operation. When performing such transfers, the terminal must possess a similar configuration as the host computer. An example hardware and software configuration requires a high-performance CPU (central processing unit), increased memory, a HDD (hard disk device), wireless and/or cable interface equipment, and various types of high-performance OSS (operating systems) and terminal applications, and the like.
Also, when performing in-shop tasks, such as product re-shelving and inventory management, the status of the work of product location and inventory counts should be confirmed. In these cases, independent, portable terminal devices are acquired and operated separately from the POS (point-of-sale) terminals such as the registers located in the shop.
Meanwhile, computers and game devices conventionally use multicolored images. These multicolored images, also called alternate colors and restricted colors, as shown in FIG. 15, are images restricted to 16 colors or 256 colors, by providing an index for a specific color; that is, a color having a specific R (red), G (green), and B (blue) value.
If each color R, G, and B is represented by eight bits (256 types), then their multicolored images require a total of 24 bits. However, because the index itself also is displayed with eight bits, a compression ratio is required even though the amount of information is still great. Without extra processing, simple data compression is not practical due to the substantial volume of memory and the decreasing communications processing speed. Consequently, data compression technology becomes extremely important for multicolored images as well as with other image data and text data. Particularly, since multicolored images have their number of colors restricted, reversible compression technology, such as encoding and decoding, that is capable of reducing lost data is necessary.
Recently, industry has been focused on technology using an entropy encoder and decoder as one type of data compression method. In other words, there are those in industry using mathematical encoding and decoding to compress data. Overviews of this technology are published in, for example, Japanese Patent Laid-Open No. 62-185413, Japanese Patent Laid-Open No. 63-74324, and Japanese Patent Laid-Open No. 63-76525.
In FIG. 16, a prior-art multicolored image encoding system 50 and decoding system 60 using such technology are shown. The encoding system 50 includes a line buffer 51 and an entropy encoder 52. The input index data, that is, color pixel data 100A, is input into line buffer 51 and entropy encoder 52. This color pixel data 100A, as shown in FIG. 17, is input successively by raster scanning in horizontal scanning order. Methods of creating this color pixel data 100A, apply an index to the sequence number of the input color, as shown in FIG. 15, and a phenomenon appears that those having near index numbers, such as "1" and "2," actually have their colors greatly different from each other, and those having far index numbers, such as "100" and "200," have their colors close to each other. In order to avoid such a phenomenon, as shown in Japanese Patent Laid-Open No. 5-328142, an index system that assigns consecutive numbers to close colors is used.
The line buffer 51 in the encoding system 50 generates reference pixel data A, B, C, and D as the reference pixel generator for encoded object pixel X from the previously input color pixel data 100A (see FIG. 17). For example, line buffer 51 stores an n-line (where n, for example, is 1-5), history when scanning an image. Also, for each color pixel data 100A of the encoding object pixel X input, a series of pixel data composed of the immediately preceding pixel A and the peripheral pixels B, C, and D are output as reference pixel data 110 toward entropy encoder 52.
This entropy encoder 52 is formed using methods such as mathematical encoding or Huffman encoding. Reference pixel data 110 is used for status signals to convert the color pixel data 100A into encoded data 200.
Meanwhile, decoding system 60 is constructed including line buffer 61 and entropy decoder 62. Here, line buffer 61 and entropy decoder 62 are formed to decode and output the input encoded data 200 by a procedure entirely opposite to line buffer 51 and entropy encoder 52 of coding system 50.
In this manner, both encoding system 50 and decoding system 60, using mutually and entirely opposite algorithms, can encode color pixel data 100A into encoded data 200, and can further decode and output this encoded data 200 into color pixel data 100B and. Accordingly, this system can be used for various purposes.
In such a system, as the value of color pixel data 100A, that is, the index number, approaches the vicinity of a fixed number, its data compression rate is increased. Also, in this system, reference pixel data 110 is used as a status indicator of entropy encoder 52 and entropy decoder 62. Consequently, if the reference pixel number is substantial, the data compression rate is similarly increased. Thus, when configuring entropy encoder 52 and decoder 62, when there is a great tendency toward the probability of occurrence of the symbols 0 or 1, it is possible to increase the data compression rate. This is because, in entropy encoding technology, short encoded data is allocated for inputs having a high probability of occurrence, and relatively long encoded data is allocated for inputs having a low probability of occurrence.
In addition, run-length encoding technology is known as a means of encoding signals of the values 0 or 1. This is, as explained above, a means of increasing the data compression rate by using the tendency of the probability of occurrence of 0 or 1.
Also, in image compression technology, there is a method of rearranging index numbers according to the order of frequency of appearance, by computing the tendency of the frequencies of appearance of the object color symbols, that is, the index numbers corresponding to the colors (Japanese Patent Laid-Open No. 6-276041). Short encoded data is allocated for inputs having a high frequency of appearance, and the compression rate is increased.
When using the frequency of appearance indicated as the prior-art technology for index conversion and data compression methods shown in FIG. 15 and FIG. 18, there are those that assign numbers in the order the image data is scanned. The index conversion shown in FIG. 15 and FIG. 18 increases the compression rate to some extent, as do those using the frequency of appearance. This is because, as is clear when comparing the first section of FIG. 18, showing the index before conversion, and the last section of FIG. 18, showing the index after conversion, in indexes of small numbers a trend of concentration and an index tendency occur.
By the way, such a common method of mathematical encoding and decoding is already described in detail on p. 26-44 and p. 44-50 of the Image Encoding Standard (International Standard ISO/IEC11544), but here it is explained simply as a premised technology when developing the present invention described below.
One example of the mathematical encoding-type entropy encoder 52 used in FIG. 16 is shown in FIG. 19. Because the configuration of the mathematical decoding-type entropy decoder 62 is identical to the configuration of the entropy encoder 52, explanation of that is omitted here.
This entropy encoder 52 is configured including an mathematical computer 55 and an occurrence probability generator 56 functioning as a status recorder. Into this occurrence probability generator 56 are written status parameters necessary for determining the symbol occurrence probabilities necessary for encoding. The status parameters are specified by input status symbols. Also, the mathematical computer 55 reads data during updates of the computational parameters and outputs the addresses, referring to a status parameter table specified by these status symbols, and the data of the occurrence probability generator 56 toward the mathematical computer 55. The mathematical computer 55 converts the input color ranking data 120 into encoded data 200 based on the data inputs, and outputs. In this manner, the index-converted data, which may be the color ranking data 120, is compressed and encoded.
The conventional terminal for remote operations consist of heavy equipment having functions equivalent to the host computer, which as a result, become high-priced items. Also, the driving applications also must be unified, and if other applications are used, the exchangeability of the data becomes difficult to manage. Especially, during data transfer, it is most common to conduct the transfer using commands specific to that OS and application, and interpretation of the commands becomes impossible with machines using different OSs or applications. Thus, the conventional terminal and the host computer are not good in interfacing with other machines, other data, and the like.
Further, the conventional terminal must have a CPU with equivalent functions to be link up with the CPU used in the host computer. Because application software and the underlying OS are advancing pursuant to advances of the CPU, when the CPU of the host computer is upgraded in functionality, the application software and underlying OS, not to mention the CPU, of the terminal also must be upgraded. As a result, in addition to the costs soaring, the installation work of various types of software becomes burdensome.
In addition, because the conventional terminal downloads host computer data into the terminal, valuable data may be stolen if the terminal is stolen. Also, because the compatibility with the data in the host computer is lost if the data is tampered with on the terminal end, a great deal of consideration must be made regarding the handling of the data. That is, data security operations are necessary and a nuisance.
Also, when performing product re-shelving operations and inventory management operations, which are conventional in-shop tasks, it is necessary to acquire portable terminals separately from the POS terminals, and operators also must be appropriately positioned. Thus, the cost of human resources increases, and it becomes an expensive system. Also, because the number of POS terminals furnished is determined based on the number of afternoon, evening and weekend customers, the POS terminals are vacant during other time slots when there are fewer customers. Because conventional portable terminals are unrelated to POS terminals, and they execute applications independently, they do not cure the inactive times of the POS terminals.
Furthermore, the conventional image data compression technology using reference pixel data has a relatively high compression rate, and it is necessary to use an encoding parameter table of a size comparable to the number of states of the reference pixel data. Therefore, as the number of reference pixels is increased in order to handle the increased compression rate, the parameter tables for encoding and decoding increase. Accordingly, the problem is created that the entropy encoder 52 and entropy decoder 62 become large-scale and more expensive.
Meanwhile, methods of sorting index numbers in order of frequency of appearance by computing the tendency of frequency of appearance of the index numbers corresponding to the colors, and methods of assigning numbers in the order of the image data scanned are desirable as simple index conversions for increasing the compression rate. However, in spite of the images generally having a tendency due to their positions on the screen, making the objects and colors (indexes) of the whole screen is necessary, and the actual compression rate is small.
The present invention aims to provide a data transmitter and data receiver, along with a data transmitter/receiver apparatus, which, in addition to being able to make the terminal lighter, reduces concerns of data theft or of the CPU becoming obsolete. Installation work of applications, etc., and allowances for security are not required. Also, the present invention aims to provide a data transmitter and data receiver, along with a data transmitter/receiver apparatus, which is capable of transmitting and receiving compressed data easily and efficiently. Furthermore, the present invention aims to provide a data compression method which is capable of compressing bit-mapped data easily and efficiently.